1. Field of the Invention
The present invention relates to an image display apparatus for projecting and displaying a wide-field-angle, high-definition image on the retina of an eye.
2. Description of the Related Art
In a conventional image display apparatus (not shown), an image display unit and the retina of an observer's eye are conjugate with each other. Accordingly, an image generated by the display unit is transmitted through an image transmission medium, and then formed on the retina by means of the optical system of the eye.
In the image display unit of this type, it is difficult to attain both wide-field-angle and high-definition simultaneously. If the image generated and displayed by the image display unit is enlarged in order to obtain a wide-field-angle, the spatial resolution would be lowered and corresponding image quality would be degraded remarkably. For example, each pixel of the image display unit may be enlarged to be visible or the spacial frequency of the image formed on the retina may be limited.
In the conventional image display apparatus, moreover, the quality of a retinal image depends on the refractive power of the observer's eye. Therefore, the refractive power of the ametropic eye must be corrected, in many ways, such as with spectacles, contact lenses, visibility adjustment equipment, or the like.
Proposed in Jpn. Pat. Appln. No. 4-302160 (U.S. Pat. No. 08/150,358), which the assignee of the present application filed, is an apparatus which projects and displays a wide-field-angle, high-definition image on the retina without being limited by the resolution of the image display unit or the optical properties of the eye.
This apparatus has the following principle of operation. A plurality of coherent point light source pairs generated and displayed by the image display unit are focused on the pupil plane of the eye with optical means, whereby a number of interference fringes are formed on the retina. These interference fringes are synthesized to form a retinal image.
According to this principle, the image display unit and the retina are not conjugate with each other, so that the spatial resolution characteristics of the optical system are not limited by those of the display unit itself. Thus, the image can be displayed in a high contrast even at high spatial frequencies.
The field-angle can be determined independently of the spatial resolution characteristics and is simply based on the F-number of an eyepiece or the size of the pixels of the image display. Thus, a wide-field-angle, high-definition image can be projected and displayed on the retina.
Utilizing the effect of optical interference, however, the above-described apparatus is subject to the following drawback. When the observers eye moves, the the phase of the interference fringes which constitute the image is changed. Since the rate of this phase change with eye movements depends on the fringe spatial frequency, the resulting retinal image is seriously degraded. If the direction of the observer's visual axis is inevitably changed, therefore, the resulting retinal image is distorted.